Progressive burning smokeless powder coated with an organic ester

ABSTRACT

PROGRESSIVE BURNING SMOKLESS POWDER COATED WITH WATER INSOLUBLE ORGANIC ESTER MELTING BELOW ABOUT 35*C. AND BOILING ABOVE AOUT 200*C. IN WHICH NITROCELLULOSE HAS A SPECIFIC SOLUBILITY.

United States Patent O 3,704,185 PROGRESSIVE BURNING SMOKELESS POWDER COATED WITH AN ORGANIC ESTER William W. Conner, Wenonah, N.J., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del. No Drawing. Filed Mar. 1, 1965, Ser. No. 437,632 Int. Cl. C06b 19/02 U.S. Cl. 14911 7 Claims ABSTRACT OF THE DISCLOSURE Progressive burning smokeless powder coated. with water insoluble organic ester melting below about 35 C. and boiling above about 200 C. in which nitrocellulose has a specific solubility.

Smokeless powder is the name given to a propellant consisting mainly of nitrocellulose. As is well known, in order to render possible close control of the burning rate of smokeless powder to give high velocity to projectiles without high breech pressures, it has been customary to coat the particles, or grains as they are commonly called, of the smokeless powder with what is referred to as a deterrent material, explosive or non-explosive, which will retard the initial burning rate of the powder grains. Ideally the quantity of coating material which penetrates the powder grains decreases toward the interior thereof, so that as the powder burns, the successively exposed surfaces contain gradually less and less of the deterrent material, thus causing the combustion of the grains to proceed with increasing speed.

In order to effect the coating of smokeless powder grains numerous deterrent materials and processes for their application have been devised. For example, a common deterrent is dinitrotoluene. Using dinitrotoluene as the deterrent material, powder grains coated with dinitrotolucne are subjected to heat with or without the presence of moisture or water. By another method, the powder grains are coated by treatment with a solution of dinitrotoluene in benzene, the benzene evaporated, and penetration of the dinitrotoluene into the grain of powder obtained by immersing the coated powder grains in a hot water bath for several hours or several days. By still another method, using as the deterrent material dimethyldiphenyl urea alone or in admixture with dinitrotoluene, the powder grains and deterrent material are covered with water, and after mixing, heat is applied for varying periods. By still another method the powder grains are surface treated by an alkyl phthalate, either in solution or in aqueous emulsion.

Treatment of smokeless powder grains to render their combustion progressive by applying thereto deterrents and methods heretofore known, while producing the desired results to a degree, has been open to a number of objections. The deterrents heretofore used have been more or less good solvents for the nitrocellulose of the base grain and when applied on the surface of the powder grain, have penetrated varying depths into the powder grain depending upon the conditions of treatment. For example, a longer time of heating of the powder grains with the deterrent or solution of the deterrent causes a deeper penetration of the deterrent into the powder grains.

In powder grains treated with a deterrent which is a good solvent for the nitrocellulose in the powder grains, the deterrent tends to penetrate more and more deeply into the powder grains during storage, particularly during storage during hot periods of the year or in hot climates. Consequently the concentration of the deterrent on the surface of the powder grain decreases with the age and the deterrent action on the surface of the powder grain 3,704,185 Patented Nov. 28, 1972 decreases. The result thereof is that powder grains deterred by a deterrent which is a good solvent for the nitrocellulose in the powder grain, do not remain ballistically stable, i.e., the ballistics of the powder change with the age of the powder due to the disappearance of the deterrent from the surface of the powder grains.

This invention provides deterrent-coated smokeless powder having, inter alia, outstanding ballistic stability.

The smokeless powder of this invention is progressiveburning powder base grain surface-coated with a waterinsoluble organic ester, said ester melting below about 35 C., and boiling above about 200 C. and having a solubility for the nitrocellulose in said smokeless powder between about that of ethylene dimethacrylate and ethylene dipropionate. The smokeless powder of this invention is prepared by agitating the smokeless powder grains with one or more of the aforementioned esters at a temperature of about from 20 to C., the ester component usually being present in amounts of about 2 to 10% based on the weight of base grain. Preferably, the ester is introduced in the form of an emulsion in a non-solvent therefor, preferably water.

The smokeless powder compositions of the present invention are designed to be used at chamber pressures above 10,000 p.s.i. and comprise both single and double base propellants and sporting as well as military powder. The manufacture of the base grain, i.e., the grain on which the deterrents of the present invention are coated, is standard in the industry and descriptions can be found, for example, in Military Explosives Technical Manual 9-1910, 1957.

The nitrocellulose used in the base grain used for the present invention is conventional military-grade nitrocellulose having an overall nitrogen content between about 12.8 and 13.4%. A single lot of nitrocellulose having the aforementioned nitrogen content can be used or, alternately, a blend having an overall nitrogen content within the desired range can be used. In addition to nitrocellulose, other energetic ingredients such as nitroglycerin, nitroguanidine, diethylene glycol dinitrate, triethylene glycol dinitrate and others can be present.

The agitation of the base grain with the ester can be carried out in several ways. Preferably an aqueous emulsion of the ester deterrent is agitated with water-wet base grain. This procedure gives optimum uniformity of coating and optimum results. A conventional sweetie barrel such as that used in the powder industry for applying dinitrotoluene coatings is a suitable apparatus for carrying out the agitation. The base grain also can be slurried with water and the ester in an agitated tank fitted with a heating jacket or heating coils. In addition, ester either per se or as a solution or dispersion in a nonsolvent for the base grain, can be sprayed on the base grain while it is tumbled or otherwise agitated to spread the ester evenly. A continuous process can be used with, for example, the base grain being placed in one end of a rotating tubular agitator and progressing down the agitator. During its progression down the agitator the base grain enters a zone where it is sprayed with the ester, then a zone where it is heated to within the aforementioned temperature range, and finally to a discharge zone where it falls from the agitator into containers. Other operations, such as glazing with graphite, also can be carried out in the tubular agitator after the ester coating has been formed, before discharge of the glazed powder.

In the preferred procedure, when the ester is added in an emulsion in water, emulsification is effected by vigorously agitating the ester with from about 0.5 to 6, and preferably 0.8 to 1.5 times its weight of water, and about from 0.2 to 5%, and preferably 0.6 to 2% of an anionic emulsifier alone or mixed with up to an equal quantity of a non-ionic emulsifier, both based on the total weight of ester. Emulsifiers of these classes are described in Detergents and EmulsifiersUp to Date, 1963, John W. McCutcheon Inc.

Examples of emulsifiers include alkaryl sodium sulfonates such as Nacconol NRSF, Sulframin L, Sulframin NAB, Santomerse SX, Santomerse E, Santomerse 85 (dodecylbenzene sodium sulfonate), Ultrawet 3ODS, 68KN, 60L, 35KK, SK and Oronite S; alkyl sulfates such as Duponol C (sodium lauryl sulfate), sodium oleyl sulfate, sodium stearyl sulfate, Teepol, Duponol ME, Alcoterge, sodium cetyl sulfate, Conco Sulfate WA (sodium lauryl sulfate), Dehydag Wax E, Nopco 1477; alkyl aryl polyether sulfates such as Triton 770, X-301 and 202; amide sulfonates such as Stepanol AM, Stepanol ME, sulfated alkylol amides such as sulfated cocomonoethanol amide (Bull. soc. chim. France 1952, 476-80); phosphate esters such as Tergitol P-28 (sodium di(2-ethylhexyl)phosphate), Victamuls 20, 24C, 27, 89; esters of polyphosphoric acids such as Na R (P O where R is a C radical such as capryl or Z-ethylhexyl (Victawets 35B and 58B), ester and ether-linked sulfonates such as Igepon AC-78 (coconut oil acid ester of sodium isethionate), dialkyl sodium sulfosuccinates (Aerosol OT-di-2-ethylhexyl sodium sulfosuccinate).

Examples of non-ionic emulsifiers which can be used in conjunction with the anionic detergents in proportions up to 50% or more by weight of the total emulsifier include polyethenoxy ethers of alkyl phenols such as Igepals RC-76'0, DM-710, DM730 and RC-520 (alkylphenoxypoly(ethylenoxy)ethanols) and Tritons N128, N101 and N-100 (nonylphenyl polyethoxy ethanols); polyethenoxy ethers of fatty alcohols such as Tergitols 3A3, 3A6 and 3A9 (polyoxyethylated tridecyl alcohol); polyethenoxy esters such as Teox 120 (polyethenoxy tallate); polyethenoxy mercaptans such as Penetrant 100; polyethenoxy glycols such as the Tweens (polyoxyethylene sorbitan monolaurate, monopalmitate, monostearate, monooleate and trioleate); glycol esters such as the Spans (sorbitan monolaurate, monopalmitate, monostearate, tristearate, monooleate and trioleate); organic phosphate esters such as the Victamuls; and amine-acid condensates such as lauric acidisopropanol amine condensate or stearic acid-diethanolamine condensate.

If the smokeless powder grains coated by the proce dure of the present invention have perforations these perforations are not coated with any substantial quantity of the ester. While I do not wish to be limited by theoretical limitations I believe that the rapid absorption of the ester onto the outside surface of the grain prevents migration into the perforation.

The quantity of ester coated on the surface of the base grain depends on the ballistic qualities desired in the powder. In general, the quantity of ester will range between about 2% and about 10% of the weight of the base grain with the preferred quantity being from about 2.5 to about 6%. The quantity of ester of the present invention needed for obtaining desired ballistic properties is generally considerably less than the quantity of dinitrotoluene needed to obtain similar ballistic properties in conventional powder.

The temperature of coating can be varied between about C. and about 120 C. and the time of coating can be varied between about 5 minutes and about six hours depending on the ester used, the type of powder coated, the procedure employed, and the results desired. The preferred temperature lies between about 70 C. and 100 C. for about A to 1 hour.

When the preferred water-emulsion technique is used, the base grain can be water-dried after coating if preferred. Such a water-dry treatment reduces the chamber pressure of the coated powder to a level slightly below that generated by the powder not water-dried. When water-dry treatments are used they merely involve heating the coated base grain in water at about from 50 to 60 C. for about 12 to 48 hours.

As previously indicated, the organic esters used in this invention have a melting point below about 35 C., a boiling point above about 200 C. at atmospheric pressure and a solvency for the nitrocellulose in the product between about that of ethylene dimethacrylate and ethylene dipropionate, inclusive, Esters, such as dibutyl phthalate, in which the nitrocellulose is considerably more soluble, lead to ballistic instability. Esters which are substantially poorer solvents are not well enough absorbed to give required muzzle velocities at or below the maximum allowable pressure.

Solvency can often be measured visually. However, since the smokeless powder is often a blend containing some relatively insoluble factions, a convenient method for measuring solubility is as follows: A sample of the nitrocellulose is leached thoroughly with ten times its weight of 65/35 ether/ethanol, filtered, the solvent evaporated and the recovered nitrocellulose dried at 45 C. Solutions of this nitrocellulose are prepared 1% concentration by weight) in ethylene dimethacrylate, ethylene dipropionate and the ester under test. The viscosity of each is then measured in an Ostwald-Fenske viscometer. Since the solvent power of the ester is related to the viscosity of the solutions, the viscosity of the ester under test measured as described above should fall between about that of the ethylene dimethacrylate solution and that of the ethylene dipropionate solution.

Examples of esters which can be used in accordance with this invention are esters of aromatic, aliphatic, and cycloaliphatic polyols or polybasic acids with monobasic acids or monohydric alcohols, respectively, particularly the aliphatic monofunctional derivatives. The esters can be saturated, that is, free of ethylenic unsaturation as in the case of ethylene dipropionate. However, because of the outstanding chemical stability of smokeless powder made therewith, esters bearing vinyl (CH C unsaturation, and preferably two or three such substituents are particularly preferred. Examples of such preferred ethylenically unsaturated esters are the alkylene acrylates such as ethylene dimethacrylate, triethylene diacrylate and triethylene dimethacrylate as well as the allyl phthalates such as diallyl phthalate and diallyl isophthalate. 'Ethylene dimethacrylate is a particularly preferred ester because of the optimum stability of products made therewith. Particularly if the preferred aqueous emulsion coating procedure is used, the esters should be substantially water insoluble, i.e., soluble to an extent less than 10% in water at 25 C.

The powder of the present invention shows several advantages over conventionally-coated powder. It has a higher gravimetric density, thus allowing more powder to be placed in a shell of fixed size. The chemical stability, as indicated by conventional tests such as the Taliani test and the methyl violet paper (MVP) test is considerably greater. The velocity-pressure relationship is higher, thus a lower weight of charge can be used to attain the same velocity. The velocity-pressure relationship is more stable to hot storage. The flame temperature is lower, thus giving a longer barrel life.

In the following examples which describe additional methods of utilizing the invention, parts and percentages are by weight. The following abbreviations are used in the examples which follow:

EDM-ethylenedimethacrylate MVPmethyl violet paper stability test (MIL-STD-286 Method 404.1.1, June 28, 1956) TalianiTaliani stability test (MIL-STD-286, Method 406.1 (T) June 28, 1956) tExplosionHours to explosion when heated at 134.5 C.

Ballistic tests are conducted in conformity with the procedure of Ordnance Manual ORDM 608-13, December 1961, Part III.

EXAMPLE 1 The nitrocellulose used in this example is leached thoroughly with ten times its weight of 65/35 ether/alcohol and filtered. The solvent is evaporated and the nitrocellulose dried at 45 C. Solutions of this dried nitrocellulose (1% by weight) are made in ethylene dipropionate and ethylene dimethacrylate. The viscosities are measured in an Ostwald-Fenske viscometer. The solution in ethylene dipropionate has a viscosity of 69.5 centistokes and the solution in ethylene dimethacrylate has a viscosity of 167.1 centistokes.

A mixture of 100 parts of nitrocellulose containing 13.2% nitrogen, 1 part of potassium sulfate and 0.7 part of diphenylamine is converted into a perforated singlebase extruded, base grain through a 0.046 OD. x 0.015 die and cut to & inch lengths by conventional means.

To 2000 parts of the above base grain slurried in 1900 parts water in a rotating sweetie barrel are added 92 parts ethylenedimethacrylate. After 15 minutes at room temperature. steam is introduced into the barrel to raise the temperature to 95100 C. for 45 minutes. The powder is removed from the barrel and dried at 80-85 C. overnight. The dry powder is glazed with graphite and screened. The final cylinder dimensions, in inches, of the powder grain are 0.030 CD. by 0.007 diam. perforation by 0.042 long.

The properties of this powder are compared with those of a conventional dinitrotoluene-coated powder (7.5% DNT coating) made in the same way.

After storage for 111 days at 150 F. and retesting, the powder of this example gained only 5400 p.s.i. in chamber pressure while the DNT-coated powder gained 8200 p.s.i. in pressure at the same weight of charge.

The following table shows ballistic test results on the powder of this example in comparison with the aforementioned DNT coated control powder and an IMR 4475 commercial powder used for 30/06, .308 and 7.62 mm. rifles. The tests are made in the same 7.62 mm. barrel using drilled cases, the charges are shot within l-2 hour period and corrected to original barrel assessment. The components are: shellFrankford Arsenal with No. 36M primer; bulletFrankford Arsenal M-80 ball, 147 grain.

Charge, Velocity, Pressure, Powder Coating grains ft.lsec. p.s.i.

IMR 4475 8% DNT 42. 0 2,713 45,000 DNT coated control 7.5% DNT 42. 0 2,705 45, 700 EDM coated powder..- 4.0% EDM 40. 5 2, 722 44, 300

EXAMPLE 2 A shotgun powder base grain is made having the following characteristics:

Composition: 100 parts nitrocellulose (13.2% nitrogen);

parts urea; 0.2 part carbon black; 0.8 part diphenylamine.

Die size, inches: 0.080 X 0.015, long.

NorE.-Final powder dimensions: 0.057 by 0.009 by 0.0008.

Powder DNT of Excoated ample 1 control Gravimetric density (g./cc.) 0.875 0. 842 MVP stability (mirL) I35 Taliani stability (mm. Hg in 5 hrs 27 157 Charge weight to give 2,720 ftJsec. in 7.62 mm.

EXAMPLES 3 THROUGH 8 The general procedure of Example 1 was repeated using the powders and coating materials noted below. The table below records the chemical stability of the products so components (grains) 4 5 0 Obtained. Calculated isoehoric flame temperature K.) 2, 824 2, 970

MVP (min.)

Talinni, 110 After 0.: mm. Hg Example 150 F. Days after 5 hrs. No. Powder Coating Initial storage storage (initial) 22 26 27 4% EDM 24 2.5% triethylene- 20 dimethacrylate. 8 4% polyester h 68 36 69 Commercial double base ball powder. IMR 4475 base grain for 7.62 mm. rifle used for making the powder oi Examples 3 through e Commercial single base powder for 7 .62 mm. riile.

d Commercial powder for 7.62 mm. rifle.

6 Experimental powder for 7.62 mm. rifle prepared as in Example 1.

f The base grain is an IMR 4350 granulation for the .30/06 rifle. Final grain dimensions 0.050 x 0.008 x 0.084 inch.

2 Not determined.

11 Polyester resin from a bisphenol and maleie or iumarie acid dissolved in styrene sold as Atlac 382-05.

7 EXAMPLES 9 AND 10 In Example 9, the water-wet base grain of Example 1 (15% total volatile) (100 parts dry basis) is charged to a sweetie barrel. An emulsion is prepared by vigorously agitating 4 parts of ethylenedimethacrylate with 4 parts of water and 0.04 part of Gafac RE610. This emulsion is added to the rotating sweeties barrel slowly over about 5 minutes; agitation is continued at room temperature for a total of 25 minutes. Steam is then introduced into the barrel while continuing agitation to raise the temperature to 8590 C. over a period of 25 minutes. Agitation is continued at 8590 C. for 30 minutes. The contents of the sweetie barrel are discharged while hot and the powder is air dried at 55 C. overnight. The dry powder is glazed and screened. The moisture content of the powder is adjusted to 1.10i0.l%.

In Example 10 the procedure above is repeated except EXAMPLES 16 AND 17 The following table shows the exceptional ballistic stability of commercial single-base propellant base grains similar to those in Example 1 coated in accordance with this invention as compared to a DNT coated standard powder after long periods of storage at 150 F. in 7.62 mm. cartridges:

8 Wks. at 150 F. 16 Wks. at 150 F. 32 Wks. at 150 F.

Charge, Velocity, Pressure, Velocity, Pressure, Velocity, Pressure grains Coating f.p.s. p.s.i. i.p.s. p.s.i. f.p.s. p.s.i.

Example 16 41.8 4.0% EDM Before heat aging 2, 740 44, 900 2, 701 44, 600 2, 715 44, 500 After heat aging. 2, 736 46, 200 2, 707 46, 100 2, 703 45, 900 Change 4 +1, 300 +6 +1, 500 +12 +1, 400 Example 17 42.0 4.5% EDM Before heat aging. 2, 725 42, 800 2, 681 41, 000 2, 687 40, 600 After heat aging 2, 716 43, 400 2, 718 44, 800 2, 731 47, 100 Change 0 600 +37 +3, 800 +44 +6, 500 Control Before heat aging. 2, 758 50, 700 2, 740 49, 800 2, 741 49, 500 After heat aging 2, 791 58, 100 2, 762 58, 600 2, 829 71, 900 Change +33 +7, 400 +22 +8, 800 +88 +22, 400

that the product is water-dried for one day before glazing.

The control is prepared by the procedure of Example I claim:

9 except that 8.5% DNT is substituted for the ethylene dimethacrylate.

The properties of the products are:

Example 0 Example 10 Control Ballistics:

Charge wt., grains 42. 5 41.5 41. 5 Velocity, fin/soc. 2, 703 2, 700 2, 703 Pressure, p.s.i 42, 300 41, 500 48, 400 Stability:

MVP, min 45 Explosion, hrs 80 survival, days 58-126 Taliani, mm. Hg. 300 min 120 Several organic esters are evaluated as solvents for nitrocellulose, Military Blend 13.15% nitrogen. Twenty parts of the deterrent and 3.2 parts of ethanol-wet nitro cellulose volatiles) are mixed by hand. The quality of solution is estimated visually from the quantity of haze and grain present. The following table shows several suitable esters arranged in order of decreasing solvent powder. The relative solvency also can be estimated more quantitatively from viscosity measurements as described hereinbefore. Powders are coated with these deterrents as described in Example 9.

The deterrent rating is calculated by determining the ballistics of powder coated with 4% of the deterrent after several days storage at ambient conditions and after days storage at 150 F. Each powder is fired at a constant velocity against a standard. The difference between the pressure of the ester-coated powders under ambient conditions from the standard is algebraically added to the increase in pressure of the ester-coated powder on heat aging. The more negative the result the better the powder.

1. Progressive burning smokeless powder coated with water-insoluble organic ester melting below about 35 C. and boiling above about 200 C., the solubility of nitrocellulose in said powder in said ester being between about that in ethylene dimethacrylate and that in ethylene dipropionate.

2. Progressive burning smokeless powder made from base grain coated with about from 2 to 10% based on the weight of said base grain of at least one of the group consisting of ethylene dipropionate, ethylene dimethacrylate, triethylene diacrylate, diallyl phthalate and triethylene dimethacrylate.

3. A powder of claim 2 wherein said ester is ethylene dimethacrylate.

4. A powder of claim 2 wherein said ester is ethylene dipropionate.

5. A powder of claim 2 wherein said ester is diallyl phthalate.

6. A process which comprises agitating smokeless powder base grains with organic ester at a temperature of about from 20 to 120 C., said ester having a melting point below 35 C. and a boiling point above 200 C., the nitrocellulose in said base grain having a solubility in said ester between about that in ethylene dimethacrylate and that in ethylene dipropionate, inclusive.

7. A process of claim 6 wherein about 2 to 10% by weight, based on the weight of base grain, of said ester emulsified in water is agitated with said base grains at a temperature of about from 70 to C.

References Cited UNITED STATES PATENTS 2,179,312 11/1939 Allison 14910 2,304,037 12/1942 Thompson et a1. 149-11 2,432,578 12/ 1947 Lindsten 14911 3,108,916 10/1963 Coffee et al 149- 10 X BENJAMIN R. PADGETT, Primary Examiner U.S. Cl. X.R. 14910, 96 

